Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS4732158 A
Publication typeGrant
Application numberUS 06/316,065
Publication dateMar 22, 1988
Filing dateOct 28, 1981
Priority dateNov 12, 1980
Fee statusLapsed
Also published asDE3144659A1
Publication number06316065, 316065, US 4732158 A, US 4732158A, US-A-4732158, US4732158 A, US4732158A
InventorsDror Sadeh
Original AssigneeRamot University Authority For Applied Research & Industrial Development Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method and apparatus for monitoring electrocardiogram (ECG) signals
US 4732158 A
Abstract
A method and apparatus for monitoring ECG signals are described characterized in that an ECG signal wave is detected, filtered to pass only a frequency band within a range of about 25-300 Hz, and stored in a first storage device; and each successive ECG signal wave is then detected, similarly filtered, and stored in a second storage device. Each of the successive signal waves, when stored in the second storage device, is cross-correlated with the signal wave stored in the first storage device, and a determination is made whether the maximum cross-correlation coefficient exceeds a predetermined value. Each of the successive signal waves having a maximum cross-correlation coefficient exceeding the predetermined value is averaged with the waves stored in the first storage device following which it is stored in the first storage device in place of the signal wave previously stored therein, and is also displayed.
Images(2)
Previous page
Next page
Claims(15)
What is claimed is:
1. A method of monitoring ECG signals, characterized in:
detecting a first ECG signal wave, filtering same to pass only a frequency band within a range of about 25-300 Hz, and storing the filtered signal wave in a first storage device;
detecting each successive ECG signal wave, similarly filtering same to pass only a frequency band within the range of about 25-300 Hz, and storing the filtered signal wave in a second storage device;
cross-correlating each of said successive signal waves, when stored in said second storage device, with the signal wave stored in said first storage device, and determining whether the maximum cross-correlation coefficient exceeds a predetermined value;
averaging, with said signal waves stored in said first storage device, each of said successive signal waves having a maximum cross-correlation coefficient exceeding said predetermined value, and storing the averaged signal wave in said first storage device in place of the signal wave previously stored therein;
and displaying the average signal wave stored in said first storage device.
2. The method according to claim 1, wherein only the PQRS segment of the first ECG signal wave, and each successive ECG signal wave, is detected, filtered and cross-correlated.
3. The method according to claim 1, wherein said predetermined maximum cross-correlation coefficient is at least 80%.
4. The method according to claim 1, wherein said first ECG signal wave, and each successive ECG signal wave, is digitized and Fast-Fourier Transformed before being filtered, and inverse Fast-Fourier Transformed after being filtered and before being stored in its respective storage device.
5. The method according to claim 1, wherein the detected ECG signal waves are filtered to pass a frequency band within the range of about 40-200 Hz to detect particularly the HIS-bundle.
6. The method according to claim 1, wherein the detected ECG signal waves are filtered to pass a frequency band within the range of about 80-200 Hz, to detect particularly small infarcts.
7. The method according to claim 1, wherein the detected ECG signal waves are filtered to pass a frequency band within the range of about 25-100 Hz, to detect particularly late-potential activity.
8. Apparatus for monitoring ECG signals, characterized in that it includes:
detecting means for detecting successive ECG signal waves;
filter means for filtering the detected ECG signal waves to pass a frequency band within a range of about 25-300 Hz;
first and second storage devices;
means for initially storing the first detected and filtered ECG signal wave in said first storage device, and for storing each successive filtered ECG signal wave in said second storage device;
cross-correlation means for cross-correlating each signal wave stored in said second storage device with that stored in said first storage device, and for including means determlning whether the maximum cross-correlation coefficient exceeds a predetermined value;
averaging means for averaging, with the signal wave stored in said first storage device, each of said successive signal waves having a maximum cross-correlation coefficient exceeding said predetermined value, and for storing the averaged signal wave in the first storage device in place of the signal wave previously stored therein;
and display means for displaying the averaged signal wave stored in said first storage device.
9. Apparatus according to claim 8, further including a digitizer for digitizing each of said ECG signal waves before it is filtered by the filtering means.
10. Apparatus according to claim 8, further including
Fast-Fourier Transform means for transforming each ECG signal wave from the time domain into the frequency domain before being filtered;
and inverse Fast-Fourier Transform means for transforming the filtered ECG signal wave from the frequency domain back to the time domain after being filtered and before being stored in its respective storage device.
11. Apparatus according to claim 8, wherein said detecting means detects only the PQRS segment of each ECG signal wave.
12. Apparatus according to claim 8, wherein said averaging means averages, with the signal wave stored in said first storage device, each of said successive signal waves having a maximum cross-correlation coefficient exceeding 80%.
13. Apparatus according to claim 8, wherein said filter means passes only a frequency band within the range of about 40-200 Hz, to detect particularly the HIS-bundle.
14. Apparatus according to claim 8, wherein said filter means passes only a frequency band within the range of about 80-200 Hz, to detect particularly small infarcts.
15. Apparatus according to claim 8, wherein said filter means passes only a frequency band within the range of about 25-100 Hz, to detect particularly late-potential activity.
Description
BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for-monitoring electrocardiogram (ECG) signals as an aid in studying and diagnosing abnormal heart activity.

ECG signals are electrical potential traces or waves accompanied by the contraction of the different cavities of the heart. They are an important aid in the study and diagnosis of abnormal heart activity. A typical ECG signal, produced by placing electrodes against the patient's skin, includes P, Q, R, S and T waves, which are all easily discernable by existing equipment. Thus, these ECG signals are commonly measured by a pen on paper at frequencies of 0-50 Hz, this frequency range being normally sufficient for discerning the above waves since the heartbeat rate is approximately 1 second, and the rise time of these waves is in the order of 0.1 second.

BRIEF SUMMARY OF THE INVENTION

The present invention is based on the physiological discovery that patients suffering from an infarct condition, and certain other heart disorders, show very small but fast changes in their ECG signal waves. If the infarct or the damage in the heart muscle is extensive, it can be seen in the usual ECG monitored by existing equipment; but if the infarct is small, it causes a minute change in the flow of electricity in the heart, producing a fast and small pulse which would not otherwise be detected by the ECG monitoring equipment.

The present invention provides a novel method and apparatus for monitoring ECG signals in order to detect these smaller-amplitude, higher-frequency waves which may indicate a small infarct or another heart disorder.

Briefly, the small, fast changes in the ECG signal waves are detected by first filtering the ECG signal via a relatively high-frequency band-pass filter in order to remove low-frequency components, namely the P, Q, R, S and T waves, and then cross-correlating successive ones of the filtered waves. The cross-correlation is performed in order to determine the exact phase of each ECG signal wave, so that many can be added together in order to add coherently the small infarct-related, or other heart-disorder-related, signals, while noise-related signals are averaged out. As many waves as required may thus be averaged to see the disorder-related signals. For example, it has been found that approximately 100 ECG signal waves are sufficient to build up the small, fast pulses in order to detect them above the electronic and physiological noise.

More particularly, and according to one broad aspect of the present invention, there is provided a method of monitoring ECG signals, characterized in detecting a first ECG signal wave, filtering same to pass only a frequency band within a range of about 25-300 Hz, and storing the filtered signal wave in a first storage device; detecting each successive ECG signal wave, similarly filtering same to pass only a frequency band within the range of about 25-300 Hz, and storing the filtered signal wave in a second storage device; cross-correlating each of said successive signal waves, when stored in said second storage device, with the signal wave stored in said first storage device, and determining whether the maximum cross-correlation coefficient exceeds a predetermined value; averaging, with said signal waves stored in said first storage device, each of said successive signal waves having a maximum cross-correlation coefficient exceeding said predetermined value, and storing the averaged signal wave in said first storage device in place of the signal wave previously stored therein; and displaying the average signal wave stored in said first storage device.

In the preferred embodiment of the invention described below, the first ECG signal wave, and each successive ECG signal wave, is digitized and Fast-Fourier Transformed before being filtered, and inverse Fast-Fourier Transformed after being filtered and before being stored in its respective storag device.

According to other aspects of the invention, there is provided apparatus for performing the above method.

The invention thus enables the detection of very small and fast pulses in ECG signals which would otherwise not be detectable in the usual ECG monitoring equipment. Thus, the present invention has been found to enable the detection of pulses having an amplitude of less than one-fifth that of the electronic noise in the instrument, which pulses would therefore be completely masked by the noise in the usual instrument. In addition, the present invention enables the detection of very fast pulses, e.g., over 50 Hz, which would otherwise be undetected by the usual ECG equipment which cuts-out at about 50 Hz. It has been found that the HIS-bundle may be detected by using a frequency band-pass within the range of about 40-200 Hz; that small infarcts may be detected by using a frequency band-pass within the range of about 80-200 Hz; and that late potential activity may be detected by using a frequency band-pass within the range of about 25-100 Hz.

Further features and advantages of the invention will be apparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by the way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a system block diagram illustrating one form of apparatus constructed in accordance with the invention;

FIG. 2 is a flow chart illustrating one method of operating the apparatus of FIG. 1 in order to monitor ECG signals in accordance with the invention; and

FIG. 3 illustrates the display produced by the apparatus of FIG. 1, including a first waveform (curve A) representing the detect ECG signal (idealized), and a second waveform (curve B) representing the signal after it has been processed in accordance with the method of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The apparatus illustrated in FIG. 1 or the drawings comprises the conventional skin electrodes, generally designated 2, placed in contact with the patient's skin at the usual locations to sense the electrical potentials accompanying the contraction of the heart cavities and to produce the ECG signals. The illustrated apparatus also includes the conventional amplifier 4 for amplifying the ECG signals.

The apparatus further includes a digitizer 6 which digitizes the detected ECG signals and a PQRS segmentizer 8 which extracts the data relating to the PQRS waves and arranges the data so that this segment is in the center. The digitized and segmented data is then fed to a Fast-Fourier Transform circuit (FFT) 10 which converts the digitized data from the time domain to the frequency domain, so that every periodic signal wave will show up as a peak in the output from the FFT 10.

The ECG signals are then fed from the FFT 10 to a band-pass filter 12. Filter 12 passes only a specified frequency band, which can be preset as desired, in accordance with the specific disorder to be particularly examined for, as described below. The filtered signal is then fed to an inverse FFT 14 which reconverts the filtered signal from the frequency domain back to the time domain.

The output of the inverse FFT 14 may be directed, via a steering circuit 16 as controlled by control circuit 18, either to a first storage device 20, called a B-memory, or to a second storage device 22, called an I-memory. Both memories may be 1024-bit registers for storing up to 1024 samples of the digitized and filtered ECG signals. As will be described more particularly below, the B-memory 20 is initially used for storing the first ECG signal wave, and the I-memory 22 is used for temporarily storing each successive ECG wave. The contents of the two memories are cross-correlated in a cross-correlator 24 in order to determine the similarity between the two stored waves, and also to determine the phase at which they are perfectly correlated. The cross-correlation coefficient of the two waves is determined in a detector circuit 26, and the maximum cross-correlation coefficient for each such correlated wave is compared in a comparator circuit 28 with a preselected maximum value to determine the extent of identity of the two compared cross-correlated waves. The maximum cross-correlation coefficient, represented by value "Z", may be preselected and manually inputted into comparator circuit 28. If the maximum cross-correlation coefficient exceeds this predetermined value, the signal wave stored in the I-memory 22 is averaged in an averaging circuit 30 with the signal wave stored in the B-memory 20, and the averaged signal is then stored in the B-memory 20 in place of the signal previously stored therein.

It will thus be seen that the B-memory 20 is continuously updated by each successive ECG signal wave which has been found to have a maximum cross-correlation coefficient with the previous averaged signal wave exceeding a predetermined maximum as determined by the preselected value "Z". This value would preferably be at least 80%, e.g., 90%.

After a predetermined number (e.g., about 100, or more) of successive ECG signal waves have thus been processed and averaged, as determined by a counter 32, the averaged signal wave may be displayed in display unit 34.

The method of monitoring ECG signals by the use of the apparatus of FIG. 1 will be better understood by reference to the flow chart of FIG. 2.

Thus, the first ECG signal wave is filtered as described above; i.e., it is digitized in digitizer 4; the PQRS segment is extracted and centered by detector 8; the digitized wave is Fast-Fourier Transformed in FFT 10 to convert it from the time domain into the frequency domain, is filtered in filter 12 to pass only the specified band-pass, and is reconverted from the frequency domain back to the time domain; and is then stored in the B-memory 20.

The next ECG wave is similarly processed and then stored in the I-memory 22. This wave in the I-memory 22 is then cross-correlated in circuit 24 with the wave in the B-memory 20, and the cross-correlation coefficient is determined in detector 26 and compared to the predetermined value "Z" in comparator 28.

If the maximum cross-correlation coefficient exceeds the predetermined value "Z" (e.g., 90%), the signal wave in the I-memory 22 is averaged with that in the B-memory 20, and the new averaged wave is then stored in the B-memory 20 in place of the previously-stored wave.

On the other hand, if the maximum cross-corrlation coefficient is found to be less than "Z", a decision is made, via counter 32, whether the preselected number of waves (e.g., 100) have been averaged; if "no", the next succeeding ECG signal wave is then processed as described above before being stored in the I-memory 22, and then cross-correlated, and its maximum cross-correlation coefficient compared with the value "Z" to determine whether or not the signal wave is to be averaged in the B-memory 20 with the previously recorded wave.

When the preselected number (e.g., 100) of waves have been averaged, the averaged wave in the B-memory is displayed in the display unit 34 (curve B) under the original ECG signal (curve A).

FIG. 3 more particularly illustrates the two signals shown in display 34, it being appreciated that the original ECG signal of Curve A is illustrated in idealized form, and that the processed signal of Curve B represents a theoretical heart condition involving several disorders.

Thus, the processed signal (curve B), includes a small fast pulse "H" between the P and Q waves; a further small, fast pulse "I" between the Q and R waves; and a still further small, fast pulse "LP" between the S and T waves. The H-pulse represents the HIS-bundle; the I-pulse represents a small infarct; and the "LP" pulse represents late-potential activity. None of these pulses would be discernable from the original ECG signal using conventional monitoring equipment because their small amplitudes would be masked by the noise, and their high frequencies would be out of the normal equipment frequency range. As will be seen in FIG. 3, the P, Q, R, S, and T waves have been removed from the displayed averaged signal (curve B), but appear in the displayed initial signal (curve A) to show the relative phases of the "H", "I" and "LP" pulses.

As indicated earlier, the frequency band-pass of filter 12 may be preselected in accordance with the specific disorder to be examined for. In general, filter 12 would provide a frequency band-pass preferably within the range of about 25-300 Hz. However, it has been found by comparing the results of this procedure with those produced by the use of a catheter to detect the ECG signal, that the HIS-bundle may be best detected by using a frequency band-pass within the range of about 40-200 Hz; that small infarcts may be best detected by using a frequency band-pass within the range of about 80-200 Hz; and that late potential activity may be best detected by using a frequency band-pass within the range of about 25-100 Hz.

While the invention has been described with respect to one preferred embodiment, it will be appreciated that many other variations, modifications and applications of the invention may be made.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3654916 *Mar 16, 1970Apr 11, 1972Univ EdinburghApparatus for monitoring recurrent waveforms
US4121576 *Feb 9, 1977Oct 24, 1978Fred Samuel GreensiteMethod and apparatus for processing vectorcardiographic signals for enabling quantitative determination of the percentage of heart muscle tissue affected by an intervention
US4170992 *Jan 5, 1978Oct 16, 1979Hewlett-Packard CompanyFiducial point location
US4279258 *Mar 26, 1980Jul 21, 1981Roy John ERapid automatic electroencephalographic evaluation
Non-Patent Citations
Reference
1Wajszczuk et al, "Circulation", vol. 58, No. 1, Jul. 1978, pp. 95-102.
2 *Wajszczuk et al, Circulation , vol. 58, No. 1, Jul. 1978, pp. 95 102.
3Wallingford et al, "I.E.E.E. Transactions on Instrumentation and Measurement", vol. 27, No. 1, Mar. 1978, pp. 70-73.
4 *Wallingford et al, I.E.E.E. Transactions on Instrumentation and Measurement , vol. 27, No. 1, Mar. 1978, pp. 70 73.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4860265 *Jan 25, 1988Aug 22, 1989Mobil Oil CorporationSeismic trace restoration using F-K filtering
US4893632 *Apr 13, 1988Jan 16, 1990Siemens AktiengesellschaftMethod and apparatus for comparing waveform shapes of time-varying signals
US4924875 *Oct 9, 1987May 15, 1990Biometrak CorporationMethod of detecting heart disorders
US4938228 *Feb 15, 1989Jul 3, 1990Righter William HWrist worn heart rate monitor
US4947857 *Feb 1, 1989Aug 14, 1990Corazonix CorporationMethod and apparatus for analyzing and interpreting electrocardiograms using spectro-temporal mapping
US4958641 *Mar 10, 1989Sep 25, 1990Instromedix, Inc.Heart data monitoring method and apparatus
US4974598 *Mar 28, 1989Dec 4, 1990Heart Map, Inc.EKG system and method using statistical analysis of heartbeats and topographic mapping of body surface potentials
US5020540 *Aug 22, 1989Jun 4, 1991Biometrak CorporationCardiac biopotential analysis system and method
US5025794 *Aug 30, 1988Jun 25, 1991Corazonix CorporationMethod for analysis of electrocardiographic signal QRS complex
US5027824 *Dec 1, 1989Jul 2, 1991Edmond DoughertyPatient wearable
US5029082 *Feb 5, 1990Jul 2, 1991Wide Trade Foundation Ltd. & Export CorporationCorrelative analysis in multi-domain processing of cardiac signals
US5105354 *Jan 23, 1989Apr 14, 1992Nippon Kayaku Kabushiki KaishaMethod and apparatus for correlating respiration and heartbeat variability
US5139027 *Dec 3, 1990Aug 18, 1992Cinventa AktiebolagMethod of filtering an analog ecg signal
US5215098 *Aug 12, 1991Jun 1, 1993Telectronics Pacing Systems, Inc.Data compression of cardiac electrical signals using scanning correlation and temporal data compression
US5215099 *May 23, 1991Jun 1, 1993Ralph HaberlSystem and method for predicting cardiac arrhythmia utilizing frequency informatiton derived from multiple segments of the late QRS and the ST portion
US5217021 *Jul 30, 1991Jun 8, 1993Telectronics Pacing Systems, Inc.Detection of cardiac arrhythmias using correlation of a cardiac electrical signals and temporal data compression
US5271411 *Sep 10, 1991Dec 21, 1993Colin Electronics Co., Ltd.Method and apparatus for ECG signal analysis and cardiac arrhythmia detection
US5479933 *Jun 23, 1994Jan 2, 1996Siemens Elema AbMethod and apparatus for processing ECG signals
US5503159 *Mar 17, 1995Apr 2, 1996Hewlett-Packard CompanyMethod for enhancement of late potentials measurements
US5564428 *Jul 7, 1994Oct 15, 1996Siemens-Elema AbMethod and apparatus for enhancing the signal-to-noise ratio of ECG signals
US5605159 *Feb 16, 1996Feb 25, 1997Smith; Joseph M.System and method for determining spatial organization of atrial activation
US5609158 *May 1, 1995Mar 11, 1997Arrhythmia Research Technology, Inc.Apparatus and method for predicting cardiac arrhythmia by detection of micropotentials and analysis of all ECG segments and intervals
US5657398 *May 8, 1995Aug 12, 1997Protocol Systems, Inc.High-quality, low-bit-rate method of compressing waveform data
US6070097 *Dec 30, 1998May 30, 2000General Electric CompanyMethod for generating a gating signal for cardiac MRI
US7151957Dec 28, 2000Dec 19, 2006Bsp Biological Signal Processing Ltd.Method and device for analyzing a periodic or semi-periodic signal
US7245960 *Aug 28, 2003Jul 17, 2007Pioneer CorporationSystem, method, program, and medium for measuring heart rate
US8874237 *Apr 16, 2008Oct 28, 2014Medtronic, Inc.Delivery catheter including side port and electrodes
EP0634136A1 *Jun 16, 1994Jan 18, 1995Siemens Elema ABMethod and device for processing ECG-signals
EP1393673A1 *Aug 26, 2003Mar 3, 2004Pioneer CorporationSystem, method, program, and medium for measuring heart rate
WO1991002484A1 *Mar 13, 1990Feb 23, 1991Biometrak CorpCardiac biopotential analysis system and method
WO1992005831A1 *Oct 8, 1990Apr 16, 1992Erwin Roy JohnEkg system using statistic and topographic mapping
WO1992009233A1 *Dec 3, 1991Jun 11, 1992Cinventa AbMethod of filtering an analog ecg signal
WO2014102653A1 *Dec 13, 2013Jul 3, 2014Koninklijke Philips N.V.Method and apparatus for reducing motion artifacts in ecg signals
Classifications
U.S. Classification600/515
International ClassificationG06F17/00, A61B5/0452
Cooperative ClassificationA61B5/7257, A61B5/04525
European ClassificationA61B5/0452B
Legal Events
DateCodeEventDescription
May 30, 2000FPExpired due to failure to pay maintenance fee
Effective date: 20000322
Mar 19, 2000LAPSLapse for failure to pay maintenance fees
Oct 12, 1999REMIMaintenance fee reminder mailed
Sep 16, 1991FPAYFee payment
Year of fee payment: 4
Oct 28, 1981ASAssignment
Owner name: RAMOT UNIVERSITY AUTHORITY FOR APPLIED RESEARCH &
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SADEH, DROR;REEL/FRAME:003949/0873
Effective date: 19811022
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SADEH, DROR;REEL/FRAME:003949/0873